Conventional plastic blow molded containers for holding carbonated beverages that pressurize the container for the most part in the past have been manufactured as base cup containers wherein the lower extremity of the blow molded container has a hemispherical shape that is received within an injection molded plastic base cup which supports the container during use. Such a base cup permits the hemispherical shape to be utilized to provide the requisite strength for withstanding the internal pressure while still providing a flat surface on which the container can be supported in an upright position. While such containers function satisfactorily, there is a cost involved in both manufacturing and assembling the base cup to the blow molded container and such cost must necessarily be included in the price to the consumer.
Blow molded containers capable of withstanding pressure have also been manufactured with freestanding base structures that are unitary with the container body such as disclosed by U.S. Pat. Nos. 3,598,270 Adomaitis; 3,727,783 Carmichael; 3,759,410 Uhilig; 3,871,541 Adomaitis; and 3,935,955 Das. These patents disclose relatively early attempts to design a freestanding blow molded container capable of withstanding internal pressure by the provision of circumferentially spaced legs having lower feet on which the container is supported.
More recent plastic blow molded containers having freestanding base structures are disclosed by German Offenlegungsschrift 29 20 122 and by U.S. Pat. Nos. 4,249,667 Pocock et al; 4,267,144 Collette et al; 4,276,987 Michel; 4,294,366 Chang; 4,318,489 Snyder et al; 4,335,821 Collette et al; 4,368,825 Motill; 4,785,949 Krishnakumar et al; 4,785,950 Miller et al; 4,850,494 Howard, Jr.; 4,850,493 Howard, Jr.; 4,867,323 Powers; and 4,910,054 Collette et al.
Certain of the containers disclosed by the above patents have flat feet on which the freestanding base structure is supported. However, some of the structures involved deflect under the pressure such that it is necessary to incline the lower feet upwardly in an inward direction as disclosed by U.S. Pat. No. 4,865,206 Behm et al so that the feet deflect downwardly to a coplanar relationship with each other upon being subjected to the internal pressure when the container is filled.
Also, United Kingdom patent application GB2189214A discloses a plastic blow molded container having a unitary base structure with a recess defined by a peripheral wall and a convex bottom wall. This recess is disclosed as functioning to centralize the preform used to blow mold the container and to also prevent the lower gate area through which the preform is injection molded from becoming the lowest portion of the container in a manner that could adversely affect stability.